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Use Cases
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Resources
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Pricing
460 BC - 370 BC
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384 BC - 322 BC
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300 BC - 500
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600 - 700
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1500 - 1590
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1600 - 1700
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1667 - 1700
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1743 - 1794
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1752
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1754
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1766 - 1844
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A. Matter is made up of atoms that are indivisible and indestructible.
B. All atoms of an element are identical. (Known now to be untrue!)
C. Atoms of different elements have different weights and different chemical properties.
D. Atoms of different elements combine in simple whole numbers to form compounds.
E. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.
1861 - 1880
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A. Cathode Ray Tube (CRT)
CRT – a glass tube that is evacuated (contains no air or matter) coated with fluorescent paint. When connected to a battery, the paint glows, indicating that there is some type of radiation streaming from the battery (the cathode)
B. Paddle wheel placed in CRT:
When Crookes placed a paddle wheel in the CRT and turned on the battery, the wheel spun. Since the tube was evacuated, this told Crookes that the Cathode Ray has mass.
1898
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A. Continued experimenting on the CRT:
JJ Thomson used charged plates to deflect the cathode ray. Found the ray deflected away from the negative plate, and toward the positive.
B. Deduced that the cathode ray was made of:
Negative particles. He named them electrons.
1900 - 1905
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A. @ 1900: Classification of radiation
B. @ 1910: Famous Gold Foil Experiment
1. What he did:
- Stretched a sheet of gold foil in a tin can and coated the inside of the can with fluorescent paint.
- Aimed a ray of alpha radiation (+ charges) at the foil.
- Expected that the alpha rays would pass right through the metal atoms in the foil, and the
fluorescent coating would light up right behind the foil.
2. What he observed:
- 99.9% of the time, the ray lit up the can right behind the foil.
- .1% of the time, the ray lit up the can OPPOSITE the foil. (behind the alpha source)
- This told him that the ray had hit something massive and dense in the center of the atom.
3. What he deduced:
A. Atoms are mostly empty space.
B. There must be a solid core in the center of the atom.
C. The core must be positively charged, since it deflected an alpha ray
1903
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1903
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1905 - 1910
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1910
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1935
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